MadSci Network: Chemistry |
The orderly structure of starch granules breaks up when they are held in hot water. At first they swell and then they gelatinize, that is the granules rupture, and the components disperse. Starch is a mixture of two polysaccharides, amylose and amylopectin, each of which is a mixture of chains of various lengths, all of high molecular weight. Most of the characteristics of starch degredation process can be explained in the terms of the activities of two enzymes: alpha amylase and beta amylase. Alpha amylase, acting on its own, is able to degrade starch to a complex mixture of sugars (including glucose and maltose), oligosaccharides and dextrins. This degradation occurs more rapidly if beta amylase is present. Whenever a starch chain is broken by alpha amylase, a new non- reducing chain end of the starch chain is formed and will be attacked by beta amylase. So since alpha amylase can cleave chains on either side of the starch molecule it can "by-pass" branches that beta amylase could then degrade these chains. Therefore, acting together, these enzymes degrade starch more rapidly and fully. It is this concept that can explain why an elivated amylase enzyme concentration (both alpha and beta) would cleave down starch molecules rapidly.
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